With a 4.56 rear in overdrive (0.70) your overall ratio is 3.192. Not bad at all. I've owned many cars/trucks before overdrive became available with 3.0 up to 3.55 rears. Your truck will be fine. You might not be able to handle the increased performance!

 

I have 33s and 4.10s (the gears were stock) and it seems a perfect ratio to me. The tires give me an equivalent ratio in the 3.80s vs the stock 245/70R17. The truck has plenty of go (it will burn rubber excessively, even with the new Auburn limited slip installed and 500# in the bed) with those gears and does 0-60 under 8 seconds. I don't note a difference in towing ability from the OE tires.

I have noted that the latest model payload package trucks have 3.73:1 ratios (and a 9.75 axle!) rather 4.10s (and a 10.25). Those new trucks offer the best mpg in that payload package category and I can't help but think the gearing is part of that.

According to a BSFC chart for an '05 engine, the best economy comes at 1997 rpm, but there is a range, from there to 3000 rpm, where it goes up minimally (from 0.436814 lb/hp-hr to 0.454492 lb/hp-hr). From three grand it jumps sharply (0.50724 @ 3400). You'd have to test to know for sure, but if you keep the rpms between 2 and 3000 rpms (at the lower end would be better). It just so happens that the 4.10/33-inch tire combo offers 2000 rpm @ 70 mph. My steady mpg drops sharply above 65 mph becausethe the truck is pushing so much air (winch bumper) but I'd guess it's doing about as good as it can.

Of course, BSFC is mostly useful for plotting MPG at a load. It's less useful for an empty truck but still a geneal pointer.

 

So someone who has the stock 3.55 ls ratio and is running 33's, would see an improvement in gas mileage switching to 4.56?

 

I have an 04 5.4 with 315/70/17 tires and 3.73 gears. It feels fine to me and I have taken it off road and towed a 3000# trailer. I bought a gryphon and am running the canned tunes on level 2 until I get my custom tunes. I probably lost about 1 mpg with the tires and I don't know if it's just me but I think I lost another mpg with the tuner on level 2. Anyways, just saying 3.73s feel fine. I may go to a 4.10 at most so I don't lose too much gas mileage since it's my daily driver.

 

I'm the guy with the 4.88s and stock tires. I also had a Retroit TruTrac differential installed to. I love the whole setup. I had the same gears in the front to run 4WD. It goes thru deep snow like it's nothing. If u want to know what it's like turn off the OD and drive around. I'm at about 3000 rpm at 70 mph.

 

How did that effect your gas mileage?

 

I run a lo of 10.0 up to 11.7.

 

Jeez, 10-11 mpg. That's city driving I'm assuming.

 

Yep that's about it with a little on the freeway at times.

 

well i got the 4.10's and i am happy with them. i actually got the highway rpm's i THOUGHT i would get with a 4.56. it did help a lot. thanks for the input. about 2600 rpm at 75 mph makes me glad i didnt get 456's

 

Have you had the Speedometer recalculated? Causei bet at 75 you really are only doing 70, now that your final gear ratio is more than what it was stock.

 

I believe there's hand held speedometer recalculators for gears and tires. I was lucky that I could change the values and trigger for my new rear gear.

 

I did order that Edge Evo thing and programmed it for the new 4.10"s. The speedo appears to be right. I would like the Edge better if you could JUST tell it you have a different gear ratio and not have to run a #1, 2, or3 program.

 

If you NEVER plan on going bigger than 33" tires and don't really tow much (a few times a year) than go with the 4.10's. If you tow a lot and may consider a lift with ~35's than consider the 4.56's.

If you are considering the 33 inch tires get them. I put some 33's on my truck and will never get a smaller tire for this truck again. They fill out the wheel wells nicely and do a lot better in the snow and mud

 

i too was thinking about 4.56's but i have a stock 2wd truck and at 75 RPMs are at 2200 with 3.55 gears OD off around 3K or so.

but i have found alot of the 4.0 exploders have an 8.8 with 4.10s and disc brakes thats what im looking for to swap out my 3.55's

i do to much high way to get 4.56s